1. Field of Invention
The present invention relates to a system for implantation of a modular prosthesis in a bone. More particularly, the present invention relates to a system wherein a single set of trial necks can be used for trial reduction of a joint using a broach and trial reduction of the joint using a stem implant.
2. Background of the Related Art
Conventional shoulder and hip prostheses typically were unitary structures including an integral stem and neck interconnecting a head. A problem associated with conventional shoulder and hip prostheses is the need to maintain large inventories of differently configured prostheses for different patient anatomies. To reduce the required inventory of parts, assorted modular prostheses have been provided. Such systems include differently sized necks, heads and necks with different lengths and angles. While existing modular prosthesis systems allow flexibility with respect to either the neck angle or the radial offset between the head and the stem to accommodate each patient's unique anatomical requirements, improvements are still needed.
In conventional modular prosthesis systems, the male feature for the neck implant for mounting on the hip or shoulder stem does not correlate with the female feature on the broach. Therefore, to allow trial reduction of a joint with both the broach and the stem implant in place, a set of trial necks for the broach and a set of trial neck for the hip or shoulder stem are required. This is in addition to a set of neck implants for the hip or shoulder stem. Thus, it would be desirable to be able to use a single set of trial neck implants with the broach and the stem implants.
The female features in the stem implants have a very fine finish and a Morse taper. The neck implant has a matching male portion with a Morse taper and locks in the female feature via assembly of the male part in the female feature of the stem implants. The quality of locking between the stem implant and the neck implant are sensitive to notching on the mating surfaces of the neck implant and the stem implant. Thus, it is desirable that the surface of the female feature of the stem implant is protected during trial reduction of the joint using the trial neck implant.
United states patent Application Publication No. 2004/0010319 (the '319 Publication) discloses a hip stem. The stem of the '319 Publication accepts necks that may be chosen from a set of modular necks. A bushing is disclosed for insertion in the female feature of the stem. The neck implant is inserted in the bushing. The bushing is implanted in the patient and provides reduction of stress and fatigue in the neck implant. The bushing is not disposable and not used to allow a single set of trial necks to be used with the stem implant and the broach.